Underground　structures　can　significantly　affect　the　ground　motion　and　further　influence　the　seismic　design　of　aboveground　structures　around　them.　Although　this　issue　has　been　well　recognised　and　studied,　it　is　not　thoroughly　addressed　as　a　large　number　of　factors　are　involved.　This　paper　focuses　on　ground　motion　amplification　induced　by　twin　circular　tunnels　embedded　in　saturated　poroelastic　soil.　The　saturated　poroelastic　soil　is　modelled　as　a　two-phase　medium　to　consider　parameters　characterising　the　fluid　phase.　Three-dimensional　scattering　features　of　the　twin　tunnels　for　obliquely　incident　seismic　waves　are　numerically　investigated　by　a　2.5D　finite　element　and　boundary　element　hybrid　model.　It　is　shown　that　the　presence　of　the　twin　tunnels　can　lead　to　significant　modifications　of　the　free-field　motion,　in　terms　of　its　magnitude　and　distribution.　The　threedimensional　oblique　incidence　scenario　presents　a　more　general　perspective　on　the　ground　motion　amplification.　Moreover,　the　effects　of　saturated　poroelastic　soil　parameters　on　the　ground　motion　amplification,　including　soil　permeability,　groundwater　levels,　and　the　degree　of　saturation,　are　parametrically　investigated.　The　differences　in　ground　motion　amplification　patterns　between　the　saturated　poroelastic　and　dry　poroelastic　soil　scenarios　are　notable,　highlighting　the　effects　of　parameters　characterising　the　fluid　phase.